The focus of this project is to investigate the interaction between opioid peptides and the hormones that are involved with growth and regeneration in the land crab Gecarcinus lateralis. Intercellular communication mechanisms have been shown to be preserved in evolution, thus the study of G. lateralis.' neuroendocrine system should provide information on how opioids modulate hormonal release in general. The promotion and/or cessation of growth and regeneration in crabs treated with various drugs and drug antagonists (e.g., met-enkephalin, naloxone) will be monitored by periodic measurements of regenerating limbs. Observations on the effects of growth hormones and releasing factors on behavior and behavioral interaction will be made with a Videomex monitoring instrument in conjunction with an Apple IIe computer. HPLC and immunoreactivity experiments will be employed in determination of monoamines and opioid peptides present in the eyestalk ganglia. Binding experiments will be performed to determine the identity of receptors that are involved in opioidhormonal interactions. Results obtained should yield information on intercellular communication and help document the endogenous complexity which will aid in making comparisons to vertebrate biomedical application. The project will also provide a unique model for neuroendocrine behavioral mechanisms with direct applications to mental health. The project will provide student research assistants with the opportunity to be exposed to research and thus be better prepared for graduate and professional training in the biomedical science. They will be immersed in all aspects of the project, from the care of animals, the conduct and assistance of the various experiments, to report writing and presentation at national meetings.